The invention relates to zirconium-based alloys and methods for manufacturing thereof and may be used in nuclear power engineering.
E110 alloy is known in the art, which is widely used in the core of nuclear reactors, comprising 1.0 percent by wt. of niobium (Specifications TU95.166-98 “ZIRCONIUM ALLOYS IN INGOTS”). The mass content of oxygen present in E110 alloy as a natural impurity does not exceed 0.05 percent by wt. and is due to its presence in the original stock components.
In spite of good operational performance, the said alloy has some disadvantages, in particular high thermal and radiation creepage (see, M. I. Solonin, Yu. K. Bibilashvili, A. V. Nikulina et al. “The Condition of and Prospects for Development of Works on Fuel Rods and Materials for Water-Cooled Reactors in Russia”. Collection of Reports Presented at the Fifth Inter-Industry Conference on Science of Reactor Materials. V.1, p. 3-32, Dimitrovgrad, GNTs RF NIIAR, 1998).
M5 alloy is known in the art, which contains, in percent by wt.: niobium—0.81-1.2, oxygen—0.090-0.149, zirconium—the rest (“Update on the Development of Advanced Zirconium Alloys for PWR Fuel Rod Claddings”. J. P. Mardon, G. Garner, P. Beslu, D. Charquet, J. Senevat. International Topical Meeting on Light Water Reactor Fuel Performance. Portland, Oreg. Mar. 2-6, 1997. Published by the American Nuclear Society, Inc. La Grange Park, Ill. 60526, USA). This publication shows a positive effect of the sulfur impurity in M5 alloy on creepage of fuel rod cladding materials.
An optimized composition of M5 alloy is known, which contains, in addition to doping components, in percent by wt.: niobium—0.81-1.2, oxygen—0.090-0.180, at the presence of the following impurities: iron—150-600 ppm, silicon—25-120 ppm, sulfur—0-35 ppm; zirconium—the rest (Jean-Paul Mardon, Daniel Charquet and Jean Senevat “Influence of Composition and Process on Out-of-Pile and In-Pile Properties of M5 Alloy”. Twelfth International Symposium on Zirconium in the Nuclear Industry. ASTM. Jun. 15-18, 1998, Toronto, Ontario, Canada). The structure of the said alloy includes intermetallic compounds having dimensions from 100 to 200 nanometers of Zr (Nb, Fe, Cr)2 with the hexagonal lattice (a=0.54 nanometers, c=0.86 nanometers) and comprising 41±4 wt. percent of niobium and 18±3 wt. percent Fe+Cr. And the intermetallic compounds Zr (Nb, Fe, Cr)2 are present in the alloy containing 100 ppm of iron and 15 ppm of chrome.
In the said modifications of M5 alloy it is very difficult to ensure a stable chemical composition through the ingot volume due to the complexity of obtaining a uniform distribution of doping additives, in particular sulfur, having very small concentrations in an ingot. Furthermore, the presence of large (100-200 nanometers) intermetallic compounds Zr (Nb, Fe, Cr)2 in the alloy structure results in the alloy manufacturability.
A zirconium-based alloy containing 0.8-1.3 wt. percent of niobium is known, which comprises, in parts per million: iron—50-250, oxygen—1,000-1,600, carbon<200, silicon<120 and unavoidable impurities (RF Patent # 2155997, IPC7 G 21 C 3/06, 3/07, publ. on Sep. 10, 2000. Bull. #25).
The said alloy, however, is used only for manufacturing tubular claddings and tubular guides for nuclear fuel rods and may not be used for manufacturing bars, sheets and other products. Furthermore, manufacturing tubes of the said alloy required that significant number (four or more) cold rolling stages be used.
A zirconium-based alloy is known, which is used for manufacturing fuel rods for nuclear reactors cores stable to creepage and corrosion under the influence of water and steam (RF Patent # 2199600 for the invention “A zirconium-based alloy stable to creepage and corrosion induced by water and steam, a method for manufacturing thereof, and its application in a nuclear reactor”, publ. on May 20, 1999, Bull. # 14). The said alloy contains 0.7-1.3 wt. percent of niobium, 0.09-1.16 wt. percent of oxygen and 8-100 ppm of sulfur.
A method of manufacturing the said alloy is also known, according to which zirconium dioxide or sulfur-containing zirconium dioxide is added, while making the stock, to the source material. Then, an ingot of the alloy, which has the above composition, is melted. The said alloy and the method of manufacturing it are most close to the claimed invention.
The said alloy is disadvantageous in that its capability to plastic deformation is lowered due to a high (more than 0.09 wt. percent) oxygen content. This forces to develop complex technologies for pressure-processing the alloy on a special equipment. Moreover, when manufacturing the said alloy it is difficult to ensure a uniform distribution of sulfur present in an insignificant quantity through the ingot volume (Elaine Hiruo, FRAATOM: SMALL MATERIALS DIFFERENCE MIGHT EXPLAIN WHY M5 SUPERIOR TO E110. Nuclear Fuel—Apr. 16, 2001-13).
When using the known method of manufacturing the alloy, it is difficult to ensure a uniform distribution of oxygen through the ingot volume. This is conditioned by the fact that, when melting the alloy, zirconium dioxide is used, which has the melting temperature about 1,000° C. higher that the melting temperature of zirconium, as the oxygen carrier. Moreover, the zirconium dioxide dilution rate in the melt is much lower that the alloy rate of crystallization. These factors contribute to non-uniform distribution of oxygen in ingots, which may result in its poor manufacturability during the subsequent hot and cold deformation, since oxygen-enriched parts of the ingot act as the stress concentrators.